1. Field of the Invention
The present invention relates to an upper frame for construction equipment mounted to swing on a lower driving structure, which is composed of left and right side plates welded on a base plate to face each other, and a plate-shaped joint connection plate welded on the left and right side plates and the base plate.
More particularly, the present invention relates to an upper frame for construction equipment mounted to swing on a lower driving structure, in which fixing pins for supporting a boom and a boom cylinder are coupled to left and right side plates that are welded on a base plate to face each other, and a plate-shaped joint connection plate is welded on the left and right side plates and the base plate (i.e. three sides of the joint connection plate are welded), so as to support the left and right side plates by exhibiting the rigidity and flexibility against load being transferred to the fixing pins through a working device during working.
2. Description of the Prior Art
As illustrated in FIG. 1, a general tracked excavator includes a lower driving structure 1; an upper frame 2 mounted to swing on the lower driving structure 1; a cab 3 and an engine room 4 mounted in front and in the rear of the upper frame 2; a working device 11 composed of a boom 5, an arm 6, and a bucket 7 connected to the upper frame 2 and hydraulic cylinders 8, 9, and 10 driving the boom, the arm, and the bucket, respectively; and a counter weight 12 mounted in the rear of the upper frame 2 to maintain a balance of the equipment during operation.
As illustrated in FIGS. 2 to 4B, a conventional upper frame of the construction equipment includes a base plate 13 on which a swing ring gear, a swing motor, and the like, are mounted to swing the upper frame 2; left and right side plates 14 and 15 (which include inner vertical plates 14a and 15a and outer vertical plates 14b and 15b) vertically welded on the base plate 13 to face each other; fixing pins 16 and 17 fixed to upper end parts of the side plates 14 and 15 to rotatably support a boom 5; fixing pins 18 and 19 fixed to lower end parts of the side plates 14 and 15 to rotatably support a boom cylinder 8; a cylindrical upper connection member 20 having both end parts welded on inner sides of the inner vertical plates 14 and 15 to joint-connect and support the upper end parts of the side plates 14 and 15; and an angle-shaped lower connection member 21 having three sides welded on the inner sides of the inner vertical plates 14a and 15a and the base plate 13 to support the inner vertical plates 14a and 15a and the base plate 13.
According to the conventional upper frame of the construction equipment, in order to effectively distribute and support large load acting on the boom 5 during working and to reduce the weight of the boom 5, the boom 5 is rotatably fixed to the side plates 14 and 15 using the fixing pins 16 and 17.
In order to secure a safe rigidity against load being transferred from a working device during working, the upper end parts of the side plates 14 and 15 are connected together and supported by the upper connection member 20, and the lower end parts of the side plates 14 and 15 are welded on the lower connection member 21 and the base plate 13, respectively.
As illustrated in FIGS. 2 and 3, in the case where the upper connection member 20 is welded between the side plates 14 and 15 in the conventional upper frame of the construction equipment, the posture of a worker, who performs welding work along the shape of the upper connection member 20 having a cylindrical cross section, becomes unstable. Accordingly, it is difficult to secure the quality of the welded part of the upper connection member 20 against the side plates 14 and 15.
Also, in the case of developing a new model of the construction equipment, power acting on the working device may be increased to improve the operation efficiency of the construction equipment in accordance with a user's demand. In this case, it is required to increase the thickness of the side plates 14 and 15 and the dimensions (e.g. size and thickness) of the upper connection member 20 to cope with the increased power of the working device.
Accordingly, the corresponding components are specially manufactured to order, and this causes the manufacturing cost to increase.
As illustrated in FIGS. 4A and 4B, if moment is applied to both end parts of the upper connection member 20 having a regular sectional area due to the load (indicated by arrows) being transferred to the fixing pins 16 and 17 through the boom 5 during working, the same moment is applied to the welded end parts of the upper connection member 20 and the center base metal part thereof in a length direction.
In this case, since the both end parts of the upper connection member 20 are vertically welded onto the side plates 14 and 15, stress is concentrated upon the end parts which are weak in structural strength. Also, since the both end parts of the upper connection member 20 are welded parts, they are weak in fatigue strength in comparison to the center part in the length direction (e.g., the fatigue strength of the welded part amounts to about 30% of the fatigue strength of the base metal part).
Accordingly, an unnecessary margin in structural strength is generated in the center part in the length direction of the upper connection member 20.
Although not illustrated in the drawings, since the same problem occurs when moment is applied to both end parts of the lower connection member 21 due to the load being transferred to the fixing pins 16 and 17 through the boom 5 during working, the detailed description thereof will be omitted.